JP7745229B2 - Management device and power supply system - Google Patents

Description

The present disclosure relates to a management device that manages multiple storage modules connected in parallel to a power source, and a power supply system.

In recent years, relatively low-power (e.g., 48V drive) electric vehicles such as electric motorcycles, electric golf carts, electric land cars, and forklifts have become popular. Some of these electric vehicles employ power supply systems in which multiple detachable, replaceable battery packs are connected in parallel. When multiple battery packs are connected in parallel, cross currents may occur.

When disconnected battery packs are connected in parallel, control has been proposed to prevent cross currents from exceeding the rated current flowing through the battery packs or relays (see, for example, Patent Document 1). Also proposed is a control that estimates the transient voltage when disconnecting batteries connected in parallel, and turns off the relay if the rated voltage of the relay is likely to be exceeded (see, for example, Patent Document 2).

JP 2009-33936 A WO 2012/164630

When disconnected battery packs are connected in parallel during charging, the upper limit of the current or power allowed to be charged to the entire parallel system usually increases. However, due to the cross current generated by the parallel connection, the upper limit of the current or power allowed to be charged to the entire parallel system may be lower than before the parallel connection. This lower limit may have adverse effects such as increased charging time and reduced regenerative braking force.

This disclosure has been made in consideration of these circumstances, and its purpose is to provide technology that prevents a decrease in charging efficiency when charging a parallel system.

In order to solve the above problem, a management device according to one embodiment of the present disclosure is a management device that manages multiple storage modules that are connected in parallel to a power source, each connected via a switch, and that, when the switches connected to some of the multiple storage modules are on and the switches connected to the remaining storage modules are off, and at least one of the off switches is turned on, the management device is equipped with a determination unit that does not allow the switch to be turned on if the upper limit of the current or power allowed to be charged to all of the multiple storage modules when the switch is turned on is lower than a threshold value based on the upper limit before the switch was turned on.

This disclosure makes it possible to prevent a decrease in charging efficiency when charging a parallel system.

1 is a diagram illustrating an electric vehicle equipped with a power supply system according to an embodiment. FIG. 2 is a diagram showing an example of the internal configuration of the battery pack of FIG. 1 . FIG. 2 is a diagram illustrating an example of the internal configuration of a management unit in FIG. 1 . FIG. 1 is a diagram showing an example of SOC-charge upper limit current characteristics at 0° C. of a certain battery pack. FIG. 10 is a diagram for explaining a cross current between battery packs. 10 is a flowchart illustrating a process of determining whether a parallel connection is established according to the first embodiment. FIG. 10 is a diagram for explaining cross current between battery packs and convergence of OCV. 10A and 10B are diagrams for explaining an example of a change in the discharge upper limit power value of the entire parallel system before and after connecting a new battery pack. 10 is a flowchart illustrating a process of determining whether a parallel connection is established according to a second embodiment.

Figure 1 is a diagram illustrating an electric vehicle 1 equipped with a power supply system 10 according to an embodiment. The electric vehicle 1 is an electric vehicle that uses a replaceable battery pack 20 as a power source, and includes, for example, an electric motorcycle, an electric golf cart, an electric land cart, a forklift, etc. The battery pack 20 is a detachable, portable, and replaceable battery pack that is attached by the user to an attachment slot on the electric vehicle 1.

The power supply system 10 is connected to the motor 60 via the main relay RYc and the inverter 50. During power running, the inverter 50 converts the DC power supplied from the power supply system 10 into AC power and supplies it to the motor 60. During regeneration, the inverter 50 converts the AC power supplied from the motor 60 into DC power and supplies it to the power supply system 10. The motor 60 is a three-phase AC motor, and during power running, it rotates according to the AC power supplied from the inverter 50. During regeneration, the rotational energy generated by deceleration is converted into AC power and supplied to the inverter 50.

The vehicle ECU (Electronic Control Unit) 40 is a control device that controls the entire electric vehicle 1. The main relay RYc is a contactor inserted between the wiring connecting the power supply system 10 and the inverter 50. When the electric vehicle 1 is running, the vehicle ECU 40 controls the main relay RYc to the on state (closed state), electrically connecting the power supply system 10 and the power system of the electric vehicle 1. When the electric vehicle 1 is not running, the vehicle ECU 40 controls the main relay RYc to the off state (open state), electrically disconnecting the power supply system 10 and the power system of the electric vehicle 1. Note that other types of switches, such as semiconductor switches, may be used instead of relays.

The electric vehicle 1 can be connected to the charger 2 via a charging cable 5. The charger 2 is connected to a commercial power grid (hereinafter simply referred to as grid 3) and can charge the battery pack 20 in the power supply system 10 from outside the electric vehicle 1. When the charger 2 is a standard charger, it generally charges the battery pack 20 with single-phase 100/200V AC power. In this case, electrical continuity exists between the charger 2 and the battery pack 20 via the charging cable 5, the external charging relay RYo, and the AC/DC converter 70.

When charging from the charger 2, the vehicle ECU 40 controls the external charging relay RYo to the on state. Note that other types of switches, such as semiconductor switches, may be used instead of the relay. The AC/DC converter 70 includes a rectifier circuit and a DC/DC converter. The rectifier circuit rectifies the AC power supplied from the charger 2 to generate DC power. The DC/DC converter controls the current or voltage of the DC power generated by the rectifier circuit according to a current command value or voltage command value specified by the vehicle ECU 40. This enables constant current (CC) charging or constant voltage (CV) charging.

When charger 2 is a rapid charger, charger 2 rectifies AC power supplied from grid 3 to generate DC power. Rapid charging standards that can be used include, for example, CHAdeMO (registered trademark), GB/T, and Combo (Combined Charging System).

The charging cable 5, which supports rapid charging, includes a communication line in addition to a power line. The vehicle ECU 40 can transmit a current command value or a voltage command value to the charger 2 via this communication line. The charger 2 controls the current or voltage of the DC power it outputs according to the current command value or voltage command value received from the vehicle ECU 40. In this case, the AC/DC converter 70 in the electric vehicle 1 is bypassed. Note that it is also possible to bypass only the rectifier circuit of the AC/DC converter 70 and control the current or voltage of the DC power by the DC/DC converter in the AC/DC converter 70 rather than controlling it on the charger 2 side.

The example shown in Figure 1 is an example in which the battery pack 20 is charged while attached to the electric vehicle 1. In this regard, it is also possible to charge the battery pack 20 while it is separated from the electric vehicle 1. In this case, the battery pack 20 can be charged by attaching it to a charging stand outside the electric vehicle 1.

The power supply system 10 includes multiple battery packs 20a-20c and a management unit 30. The multiple battery packs 20a-20c are connected in parallel to the load (mainly the motor 60) of the electric vehicle 1. Note that the motor 60 serves as the power source for the multiple battery packs 20a-20c during regeneration. The number of battery packs 20 connected in parallel is determined according to the required capacity or output of the electric vehicle 1. While Figure 1 shows an example in which three battery packs 20a-20c are connected in parallel, this is not limited to three in parallel. More battery packs 20 may be connected in parallel to extend the cruising range. Furthermore, in the case of a small electric vehicle 1, two battery packs may be connected in parallel.

Figure 2 is a diagram showing an example of the internal configuration of the battery pack 20 of Figure 1. The battery pack 20 includes a pack relay RY1, a relay driving unit 25, a battery module M1, a shunt resistor Rs, temperature sensors T1 and T2, a voltage measurement unit 21, a temperature measurement unit 22, a current measurement unit 23, and a control unit 24. The relay driving unit 25 turns the pack relay RY1 on/off in response to a control signal received from the management unit 30 via the control unit 24.

Battery module M1 includes multiple cells E1-En connected in series. Battery module M1 may also be configured by connecting multiple cell blocks in series, each consisting of multiple cells connected in parallel. The cells may be lithium-ion battery cells, nickel-metal hydride battery cells, lead battery cells, etc. In the following, this specification assumes the use of lithium-ion battery cells (nominal voltage: 3.6-3.7V).

A shunt resistor Rs is connected in series with the multiple cells E1-En that make up the battery module M1. The shunt resistor Rs functions as a current detection element. A Hall element may be used instead of the shunt resistor Rs. In addition, multiple temperature sensors T1, T2 are installed to detect the temperature of the multiple cells E1-En. One or more temperature sensors may be installed in the battery module M1. The temperature sensors T1, T2 can be, for example, thermistors.

Multiple voltage lines connect each node of the multiple series-connected cells E1-En to the voltage measurement unit 21. The voltage measurement unit 21 measures the voltage of each cell E1-En by measuring the voltage between each two adjacent voltage lines. The voltage measurement unit 21 transmits the measured voltage of each cell E1-En to the control unit 24 via a communication line.

Because the voltage measurement unit 21 is at a high voltage relative to the control unit 24, the voltage measurement unit 21 and control unit 24 are connected by a communication line, with isolation provided as necessary. The voltage measurement unit 21 can be configured as an ASIC (Application Specific Integrated Circuit) or a general-purpose analog front-end IC. The voltage measurement unit 21 includes a multiplexer and an A/D converter. The multiplexer outputs the voltage between two adjacent voltage lines to the A/D converter in order from top to bottom. The A/D converter converts the analog voltage input from the multiplexer into a digital value.

The temperature measurement unit 22 includes a voltage dividing resistor and an A/D converter. The A/D converter sequentially converts multiple analog voltages, each divided by multiple temperature sensors T1, T2 and multiple voltage dividing resistors, into digital values and outputs them to the control unit 24. The control unit 24 estimates the temperatures of multiple cells E1-En based on these digital values.

The current measurement unit 23 includes a differential amplifier and an A/D converter. The differential amplifier amplifies the voltage across the shunt resistor Rs and outputs it to the A/D converter. The A/D converter converts the analog voltage input from the differential amplifier into a digital value and outputs it to the control unit 24. The control unit 24 estimates the current flowing through the multiple cells E1-En based on the digital value.

In addition, if an A/D converter is installed in the control unit 24 and an analog input port is installed in the control unit 24, the temperature measurement unit 22 and the current measurement unit 23 may output analog voltages to the control unit 24, which may be converted into digital values by the A/D converter in the control unit 24.

The control unit 24 manages the states of the multiple cells E1-En based on the voltage, temperature, and current of the multiple cells E1-En measured by the voltage measurement unit 21, temperature measurement unit 22, and current measurement unit 23. The control unit 24 can be configured with a microcomputer and non-volatile memory (e.g., EEPROM (Electrically Erasable Programmable Read-Only Memory), flash memory).

The microcomputer's internal memory stores an SOC (State Of Charge)-OCV (Open Circuit Voltage) map 241. The SOC-OCV map 241 describes characteristic data for the SOC-OCV curves of cells E1-En. The SOC-OCV curves of cells E1-En are created in advance based on characteristic tests conducted by the battery manufacturer and registered in the microcomputer's internal memory at the time of shipment. The SOC-OCV map 241 may also be registered in non-volatile memory. To estimate the SOC or OCV of cells E1-En with higher accuracy, the battery manufacturer may derive and map the SOC-OCV characteristics of cells E1-En for each combination of temperature category and state of health (SOH) category. Instead of a map, a function may be used in which the SOC is the target variable and the OCV, temperature, and state of health are explanatory variables.

The control unit 24 can estimate the SOC and SOH of each of the multiple cells E1-En. The control unit 24 can estimate the SOC using the OCV method or the current integration method. The OCV method is a method of estimating the SOC based on the OCV of each cell E1-En measured by the voltage measurement unit 21 and the characteristic data of the SOC-OCV curve described in the SOC-OCV map 241. The future OCV is estimated based on the voltage of each cell E1-En measured by the voltage measurement unit 21, the current of the battery module M1 measured by the current measurement unit 23, and the temperature of the battery module M1 measured by the temperature measurement unit 22. The current integration method is a method of estimating the SOC based on the OCV of each cell E1-En at the start of charge/discharge and the integrated value of the current measured by the current measurement unit 23. With the current integration method, measurement errors by the current measurement unit 23 accumulate as the charge/discharge time increases. Therefore, it is preferable to correct the SOC estimated by the current integration method using the SOC estimated by the OCV method.

SOH is defined as the ratio of the current full charge capacity to the initial full charge capacity, and the lower the value (closer to 0%), the more advanced the deterioration. SOH can be determined by measuring the capacity after full charge and discharge, or by adding together storage deterioration and cycle deterioration. Storage deterioration can be estimated based on the SOC, temperature, and storage deterioration rate. Cycle deterioration can be estimated based on the SOC range, temperature, current rate, and cycle deterioration rate used. The storage deterioration rate and cycle deterioration rate can be derived in advance through experiments or simulations. The SOC, temperature, SOC range, and current rate can be determined by measurement.

SOH can also be estimated based on its correlation with the cell's internal resistance. Internal resistance can be estimated by dividing the voltage drop that occurs when a specified current is passed through the cell for a specified time by that current value. Internal resistance decreases as temperature increases, and increases as SOH decreases.

The control unit 24 periodically transmits monitoring data including at least one of the voltage, temperature, current, SOC, SOH, and internal resistance of the multiple cells E1-En included in the battery pack 20 to the management unit 30. Communication between the control unit 24 of the battery pack 20 and the management unit 30 can be performed using, for example, serial communication conforming to the RS-485 standard. The control unit 24 of the battery pack 20 and the management unit 30 may be connected via a dedicated communication line, wirelessly, or via power line communication.

Figure 3 is a diagram showing an example of the internal configuration of the management unit 30 in Figure 1. The management unit 30 includes a processing unit 31 and a memory unit 32, and manages multiple battery packs 20a-20c.

The processing unit 31 includes an acquisition unit 311, a calculation unit 312, a judgment unit 313, and a notification unit 314. The functions of the processing unit 31 can be realized by a combination of hardware and software resources, or by hardware resources alone. Hardware resources can include CPUs, ROMs, RAMs, DSPs, ASICs, FPGAs, and other LSIs. Software resources can include programs such as firmware.

The memory unit 32 includes a non-volatile recording medium such as flash memory. The memory unit 32 stores an SOC-charge upper limit current map 322. The SOC-charge upper limit current map 322 describes characteristic data for the SOC-charge upper limit current curves of cells E1-En. The SOC-charge upper limit current curves of cells E1-En are created based on characteristic tests conducted by the battery manufacturer. The SOC-charge upper limit current curve is characteristic data that specifies, for each SOC, the upper limit of the charging current allowed for charging a cell, from the standpoint of cell protection and safety. For a typical cell, the higher the SOC, the lower the upper limit of the current allowed for charging. Note that in this specification, charging current is considered as an absolute value.

When discharging from a cell, the CCV (Closed Circuit Voltage) decreases as the discharge current increases. The CCV of a cell when discharging is defined by the following (Equation 1). When charging a cell, the CCV increases as the charging current increases. The CCV of a cell when charging is defined by the following (Equation 2).

CCVd=OCV-Id×R...(Formula 1)
CCVc=OCV+Ic×R...(Formula 2)
Id is the discharge current, Ic is the charge current, and R is the internal resistance.

As shown in Equation 2 above, as the charging current Ic increases, the CCV rises. When the CCV enters the overcharge region, the burden on the battery increases, causing deterioration. As shown in Equation 2 above, the higher the OCV, the higher the CCV. Since the higher the SOC, the higher the OCV, the lower the upper limit of the charging current Ic must be set.

The SOC-maximum charging current characteristics of cells E1-En depend on temperature and state of health (SOH). Battery manufacturers derive and map the SOC-maximum charging current characteristics of cells E1-En for each combination of temperature and state of health (SOH). The SOC-maximum charging current characteristics are registered in the control unit 24 of the battery pack 20 (e.g., in the internal memory of a microcomputer) at the time of shipment. The management unit 30 of the electric vehicle 1 acquires the SOC-maximum charging current characteristics from the control unit 24 of the battery pack 20 when the battery pack 20 is first installed in the electric vehicle 1. Note that the SOC-maximum charging power characteristics may be used instead of the SOC-maximum charging current characteristics, or both may be used. For example, the upper limit of the charging current from the charger 2 may be controlled with reference to the SOC-maximum charging current characteristics, and the upper limit of the regenerative power from the motor 60 may be controlled with reference to the SOC-maximum charging power characteristics. Furthermore, instead of a map, a function may be used with the upper limit charging current or upper limit charging power as the objective variable and the SOC, temperature, and state of health as explanatory variables.

Figure 4 shows an example of the SOC-charge upper limit current characteristics of a battery pack at 0°C. As shown in Figure 4, the higher the SOC, the lower the charge upper limit current.

Returning to Figure 3, the acquisition unit 311 acquires monitoring data including at least the voltage and SOC of cells E-En from the control unit 24 of each battery pack 20. The calculation unit 312 estimates the SOC of each battery pack 20 based on the SOC of the multiple cells E-En included in each battery pack 20. Typically, the SOC of the pack is the SOC of the lowest cell when the SOC is low, and the SOC of the highest cell when the SOC is high. Note that the calculation unit 312 may also convert the SOC of the multiple cells E-En included in the battery pack 20 into capacity, calculate the combined capacity of the multiple cells E-En, and use the SOC corresponding to this combined capacity as the SOC of the pack.

As described above, in this embodiment, a state occurs in which the pack relay RY1 connected to some of the multiple battery packs 20a-20c is on and the pack relay RY1 connected to the remaining battery packs 20 is off. When one of the off-state pack relays RY1 (hereinafter referred to as the target pack relay RY1) needs to be turned on, the calculation unit 312 estimates the upper limit of the current or power that is allowed to be charged to all of the multiple battery packs 20 (hereinafter referred to as the parallel system) when the target pack relay RY1 is turned on.

The determination unit 313 compares the upper limit value estimated by the calculation unit 312 (hereinafter referred to as the predicted upper limit value) with a threshold value based on the upper limit value of the current or power allowed to be charged into the parallel system before turning on the target pack relay RY1 (hereinafter referred to as the current upper limit value). The threshold value may be the same as the current upper limit value (adjustment value α = 0), the current upper limit value plus the adjustment value α, or the current upper limit value minus the adjustment value α. The designer can set the adjustment value α taking into account the number of parallel battery packs 20, the application, etc. If the predicted upper limit value is equal to or greater than the threshold value, the determination unit 313 permits the target pack relay RY1 to be turned on. If the predicted upper limit value is lower than the threshold value, the relay drive unit 25 does not permit the target pack relay RY1 to be turned on. If the determination unit 313 permits the target pack relay RY1 to be turned on, the relay drive unit 25 turns on the target pack relay RY1.

The notification unit 314 notifies the vehicle ECU 40 of the upper limit of the current or power allowed to be charged from the parallel system (hereinafter referred to as the upper limit charging current value or upper limit charging power value of the entire parallel system (collectively referred to as the upper limit charging value)). The management unit 30 and the vehicle ECU 40 are connected via an in-vehicle network. A CAN (Controller Area Network) or a LIN (Local Interconnect Network) can be used as the in-vehicle network. The vehicle ECU 40 controls the regenerative current or regenerative power of the motor 60 within the upper limit charging current value or upper limit charging power value of the entire parallel system received from the management unit 30. For example, when the regenerative power value of the regenerative brake reaches the upper limit charging power value of the entire parallel system, the vehicle ECU 40 switches from regenerative braking to mechanical braking. The mechanical brake converts regenerative energy into thermal energy. Furthermore, when rapid charging is performed using DC from the charger 2, the notification unit 314 notifies the charger 2 of the upper limit charging current value or upper limit charging power value of the entire parallel system.

Essentially, the more battery packs 20 connected in parallel, the higher the upper limit of charging for the entire parallel system. However, there are cases where adding a battery pack 20 to a parallel system does not increase the upper limit of charging for the entire parallel system. This is the case when the connection of a new battery pack 20 causes cross currents between multiple battery packs 20.

Figure 5 is a diagram illustrating cross currents between battery packs 20. For ease of understanding, Figure 5 shows two battery packs 20 connected in parallel. The state on the left is a state in which the first pack relay RY1 connected to the first battery pack 20a is on and the second pack relay RY1 connected to the second battery pack 20b is off, with current being supplied from the power source (e.g., charger 2) only to the first battery pack 20a. In this case, the upper limit charging current value of the entire parallel system is the same as the upper limit charging current value of the first battery pack 20a.

The state on the right side of Figure 5 shows the state after the second pack relay RY1 is turned on. If the OCV of the second battery pack 20b is higher than the CCV when charging the first battery pack 20a at the upper limit charging current value, a cross current will occur from the second battery pack 20b to the first battery pack 20a. As a result, the upper limit charging current value of the first battery pack 20a does not change, but the current that can be charged from the power source to the first battery pack 20a decreases, and the upper limit charging current value of the entire parallel system as seen from the power source decreases. If charging is being performed at the maximum current from the charger 2, charging may be stopped by control within the charger 2.

The CCV when charging the first battery pack 20a at the upper limit charging current value is an estimated value. The current charged to the first battery pack 20a fluctuates due to fluctuations in the power supply voltage, etc., and the CCV of the first battery pack 20a also fluctuates due to these influences. The CCV when charging the first battery pack 20a at the upper limit charging current value is a value that indicates the maximum voltage of the first battery pack 20a during charging.

Next, consider the case where the CCV of the first battery pack 20a when charging with the upper limit charging current value matches the OCV of the second battery pack 20b, and the second pack relay RY1 is turned on. When the current actually charging the first battery pack 20a from the power source matches the upper limit charging current value of the first battery pack 20a, the CCV of the first battery pack 20a and the OCV of the second battery pack 20b become equal. In this case, no cross current occurs between the first battery pack 20a and the second battery pack 20b, and the upper limit charging current value of the entire parallel system does not decrease.

If the current actually being charged from the power source to the first battery pack 20a is lower than the upper limit charging current value of the first battery pack 20a, the actual CCV of the first battery pack 20a will be lower than the CCV when charged at the upper limit charging current value. In this case, a cross current will occur from the second battery pack 20b to the first battery pack 20a. However, if the output current from the power source increases to the upper limit charging current value of the first battery pack 20a, the cross current will stop, and the upper limit charging current value of the entire parallel system will not decrease.

Next, consider the case where the OCV of the second battery pack 20b is lower than the CCV when charging the first battery pack 20a with the upper limit charging current value, and the second pack relay RY1 is turned on. Because the upper limit charging current value of the second battery pack 20b is greater than the upper limit charging current value of the first battery pack 20a, the upper limit charging current value of the entire parallel system does not decrease when the second pack relay RY1 is turned on.

In the above explanation, an example has been described in which the calculation unit 312 of the management unit 30 calculates both the upper limit charging current value of each battery pack 20 and the upper limit charging current value of the entire parallel system. In this regard, the upper limit charging current value of a battery pack 20 may be calculated by the control unit 24 within the battery pack 20. The control unit 24 within each battery pack 20 transmits the calculated upper limit charging current value of the battery pack 20 to the management unit 30. The calculation unit 312 of the management unit 30 calculates the upper limit charging current value of the entire parallel system based on the upper limit charging current values received from the multiple battery packs 20.

Below, we will explain two examples of the judgment process that determines whether or not to allow parallel connection of the target pack relay RY1. Example 1 is a dynamic judgment process, and Example 2 is a static judgment process.

Figure 6 is a flowchart for explaining the parallel connection determination process according to Example 1. When the power supply of the electric vehicle 1 is turned on (corresponding to turning on the ignition of an engine vehicle) (Y in S30), the determination unit 313 causes the relay drive unit 25 to turn on the pack relay RY1 connected to the battery pack 20 with the lowest OCV among the multiple battery packs 20 (S31). If there are multiple battery packs 20 with the lowest OCV, the determination unit 313 simultaneously turns on the multiple pack relays RY1 connected to those multiple battery packs 20.

During execution of parallel connection control (N in S32), the following process is executed: The determination unit 313 identifies the battery pack 20 with the lowest OCV among the battery packs 20 whose pack relay RY1 is in the off state as the next connection candidate for which pack relay RY1 should be turned on (S33).

The calculation unit 312 derives the upper limit charging current value of the battery pack 20 by referring to the SOC-charge upper limit current map 322 based on the SOC of the battery pack 20 when the pack relay RY1 is in the on state. The calculation unit 312 applies the OCV, internal resistance, and upper limit charging current value of the battery pack 20 to the above (Equation 2) to estimate the CCV corresponding to the upper limit charging current value of the battery pack 20 (S34). When deriving the SOC, internal resistance, and upper limit charging current value of the battery pack 20, the calculation unit 312 takes into account at least the temperature and SOH of the battery pack 20 as parameters.

The determination unit 313 compares the estimated CCV with the OCV of the connection candidate battery pack 20 (S35). If the estimated CCV is equal to or higher than the OCV of the connection candidate battery pack 20 (Y in S35), the determination unit 313 allows the connection of the connection candidate battery pack 20 (S36) and causes the relay drive unit 25 to turn on the pack relay RY1 connected to the connection candidate battery pack 20. If the estimated CCV is lower than the OCV of the connection candidate battery pack 20 (N in S35), the determination unit 313 does not allow the connection of the connection candidate battery pack 20 (S37). The process transitions to step S32.

When there are multiple battery packs 20 with pack relay RY1 in the ON state, the CCVs corresponding to the upper limit charging current values of the multiple battery packs 20 are the same. With the CCVs in place, the calculation unit 312 estimates the CCVs corresponding to the upper limit charging current values of the multiple battery packs 20 in the ON state.

If, in the determination of step S35, the estimated CCV is lower than the OCV of the battery pack 20 that is the candidate for connection, the battery pack 20 that is the candidate for connection cannot be connected. However, if the battery pack 20 in the ON state continues to be charged, the SOC of the battery pack 20 in the ON state increases. As the SOC increases, the OCV increases, and the CCV corresponding to the upper limit charging current value also increases. When the CCV corresponding to the upper limit charging current value increases to the OCV of the battery pack 20 that is the candidate for connection, the battery pack 20 that is the candidate for connection can be connected. Note that the CCV corresponding to the upper limit charging current value may increase due to temperature changes.

Next, a second example of the parallel connection determination process will be described. As described above, when the OCVs of multiple battery packs 20 connected in parallel are not the same, a cross current occurs from a battery pack 20 with a higher OCV to a battery pack 20 with a lower OCV. The cross current reduces the OCV of the battery pack 20 with a higher OCV and increases the OCV of the battery pack 20 with a lower OCV. When the voltage difference between the two is eliminated, the cross current stops. When the cross current stops, the OCVs of the multiple battery packs 20 connected in parallel are the same.

Figure 7 is a diagram for explaining cross currents between battery packs 20 and convergence of OCVs. For ease of understanding, Figure 7 shows two battery packs 20 connected in parallel. The state on the left shows a state in which the first pack relay RY1 connected to the first battery pack 20a is on and the second pack relay RY1 connected to the second battery pack 20b is off, indicating that the OCV of the first battery pack 20a is lower than the OCV of the second battery pack 20b.

The state on the right side of Figure 7 shows the state after the second pack relay RY1 is turned on. When the first battery pack 20a and the second battery pack 20b are conductive, current flows from the second battery pack 20b to the first battery pack 20a, causing the OCV of the second battery pack 20b to decrease and the OCV of the first battery pack 20a to increase. When the OCVs of both battery packs eventually match, the cross current from the second battery pack 20b to the first battery pack 20a stops.

Under ideal conditions where the pack capacities and other factors are consistent, the OCV of the first battery pack 20a and the second battery pack 20b when the cross current is stopped will be the average SOC of the SOC of the first battery pack 20a and the SOC of the second battery pack 20b before the cross current occurred, and the OCV when the cross current is stopped will be the OCV corresponding to this average SOC. Even when three or more battery packs 20 with mismatched OCVs are connected in parallel, under ideal conditions, the cross current will cause the OCVs of the three or more battery packs 20 to match. In this case, the OCV of the three or more battery packs 20 after the OCVs have been matched will be the average of the OCVs of the three or more battery packs 20 before the cross current occurred.

In Example 2, the calculation unit 312 estimates the upper limit charging current value of the entire parallel system at the time when the OCV converges after a new battery pack 20 is connected to the parallel system. The determination unit 313 allows connection of the new battery pack 20 when the estimated upper limit charging current value is equal to or greater than the upper limit charging current value of the entire parallel system before the new battery pack 20 was connected to the parallel system. The determination unit 313 does not allow connection of the new battery pack 20 when the estimated upper limit charging current value is lower than the upper limit charging current value of the entire parallel system before the new battery pack 20 was connected.

Figure 8 is a diagram illustrating an example of changes in the upper limit charging current value of the entire parallel system before and after connecting a new battery pack 20. For example, consider a state in which the first battery pack 20a is connected to a power source and the second battery pack 20b is not, as shown on the left side of Figure 7. The following explanation assumes that battery packs using the same type of cells are used and that the conditions regarding pack capacity, SOH, and temperature are the same. Assume that the SOC of the first battery pack 20a is 80% and the SOC of the second battery pack 20b is 90%. Referring to the SOC-upper limit charging current characteristic shown in Figure 8, the upper limit charging current value when the SOC is 80% is 15 A. The upper limit charging current value of the entire parallel system when only the first battery pack 20a is connected is also 15 A.

Next, consider the state after the second battery pack 20b is connected to the parallel system, as shown on the right side of Figure 7. When the second battery pack 20b is connected to the parallel system, a cross current occurs from the second battery pack 20b to the first battery pack 20a. The cross current causes the SOC of the second battery pack 20b to decrease and the SOC of the first battery pack 20a to increase. The cross current stops when the SOC of both battery packs reaches 85%. Referring to the SOC-maximum charging current characteristics shown in Figure 8, the maximum charging current value is 6 A when the SOC is 85%. Therefore, the maximum charging current value of the entire parallel system when the first battery pack 20a and second battery pack 20b are connected is 12 A (= 6 A x 2).

In this example, connecting the second battery pack 20b reduces the upper limit charging current of the entire parallel system from 15 A to 12 A. As shown in Figure 8, when the upper limit charging current when the SOCs are equal (SOC = 85%) is below the imaginary line connecting the upper limit charging current (15 A) of the first battery pack 20a and the upper limit charging current (2 A) of the second battery pack 20b before connecting the second battery pack 20b, the upper limit charging current of the entire parallel system is lower than the current value obtained by simply averaging the upper limit charging current (15 A) of the first battery pack 20a and the upper limit charging current (2 A) of the second battery pack 20b before connecting. Therefore, if the upper limit charging current of the entire parallel system after connecting the second battery pack 20b is estimated without reference to the SOC-upper limit charging current characteristics, the upper limit charging current may be overestimated, resulting in a situation where the actual upper limit charging current is lower than the charging current value from the charger 2.

Figure 9 is a flowchart for explaining the parallel connection determination process according to Example 2. When the power supply to the electric vehicle 1 is turned on (Y in S40), the determination unit 313 causes the relay drive unit 25 to turn on the pack relay RY1 connected to the battery pack 20 with the lowest OCV among the multiple battery packs 20 (S41). If there are multiple battery packs 20 with the lowest OCV, the determination unit 313 simultaneously turns on the multiple pack relays RY1 connected to those multiple battery packs 20.

If there is a battery pack 20 with pack relay RY1 in the OFF state while parallel connection control is being executed (N in S42), the following process is executed. The determination unit 313 identifies the battery pack 20 with the lowest OCV among the battery packs 20 with pack relay RY1 in the OFF state as the next connection candidate for which pack relay RY1 should be turned on (S43).

The calculation unit 312 estimates the convergence value of the OCV of multiple battery packs 20 connected to the parallel system when a candidate battery pack 20 for connection is turned on (S44). Based on the SOC corresponding to the converged OCV, the calculation unit 312 derives the upper limit charging current value of one battery pack 20 by referring to the SOC-upper limit charging current map 322. The calculation unit 312 multiplies the upper limit charging current value of one battery pack 20 by the number of parallel connections to estimate the upper limit charging current value of the entire parallel system (S45). When deriving the SOC and upper limit charging current value of a battery pack 20, the calculation unit 312 takes into account at least the temperature and SOH of the battery pack 20 as parameters.

The determination unit 313 determines whether the charging upper limit current value of the entire parallel system will decrease due to the connection of the candidate battery pack 20 (S46). If the charging upper limit current value of the entire parallel system will not decrease (N in S46), the determination unit 313 allows the connection of the candidate battery pack 20 (S47) and causes the relay driver 25 to turn on the pack relay RY1 connected to the candidate battery pack 20. If the charging upper limit current value of the entire parallel system will decrease (Y in S46), the determination unit 313 does not allow the connection of the candidate battery pack 20 (S48). The process proceeds to step S42.

If the determination in step S46 is that the charging upper limit current value of the entire parallel system will decrease due to the connection of the candidate battery pack 20, the candidate battery pack 20 cannot be connected. However, if the on-state battery pack 20 continues to be charged, the SOC of the on-state battery pack 20 will increase. As the SOC increases, the charging upper limit current value of the entire parallel system will also increase. Eventually, a state will be reached where the charging upper limit current value of the entire parallel system will not decrease even if the candidate battery pack 20 is connected. Furthermore, the charging upper limit current value of the entire parallel system may decrease due to temperature changes.

As described above, according to this embodiment, when the connection of a new battery pack 20 would lower the upper charge limit value of the entire parallel system, the connection of the new battery pack 20 is prohibited. This prevents an increase in charging time and waste of regenerative energy, and prevents a decrease in the charging efficiency of the battery pack 20.

The present disclosure has been described above based on embodiments. The embodiments are illustrative, and those skilled in the art will understand that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of the present disclosure.

The parallel connection determination process according to Example 1 and the parallel connection determination process according to Example 2 may be used together. In this case, if connection is permitted in both determination processes, the connection candidate battery pack 20 is connected, and if connection is not permitted in at least one of the determination processes, the connection candidate battery pack 20 is not connected. For example, even if connection of the connection candidate battery pack 20 is permitted in the determination process according to Example 2, connection may not be permitted in the determination process according to Example 1.

The determination process according to Example 2 determines whether or not a candidate battery pack 20 can be connected based on the upper charge limit value of the entire parallel system at a certain point in the future. The upper charge limit value in the process leading up to that point in time is not taken into consideration. On the other hand, the determination process according to Example 1 determines whether or not a candidate battery pack 20 can be connected based on the current upper charge limit value, which changes from moment to moment. Therefore, there may be cases where the results of the two determinations do not match. When the parallel connection determination process according to Example 1 and the parallel connection determination process according to Example 2 are used together, it is possible to further prevent a decrease in charging efficiency.

In the above-described embodiment, an example was described in which the management unit 30 is provided outside the multiple battery packs 20. In this regard, the management unit 30 may be provided inside any one of the multiple battery packs 20. In this case, the battery pack 20 that realizes the functions of the management unit 30 becomes the master device, and the remaining battery packs 20 become slave devices.

In the above-described embodiment, an example has been described in which detachable, replaceable battery packs 20 are connected in parallel. In this regard, fixed battery packs 20 may also be connected in parallel. When fixed battery packs 20 are used, the functions of multiple control units 24 and management units 30 provided in multiple battery packs 20 can be integrated. For example, multiple control units 24 and management units 30 may be realized by a single microcomputer.

In the above-described embodiment, an example has been described in which a battery pack 20 incorporating a battery module M1 including lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, etc. has been used. In this regard, a capacitor pack incorporating a capacitor module including electric double-layer capacitor cells, lithium-ion capacitor cells, etc. may also be used. In this specification, battery modules and capacitor modules are collectively referred to as energy storage modules, and battery packs and capacitor packs are collectively referred to as energy storage packs.

In the above-described embodiment, an example of connecting detachable, replaceable energy storage packs in parallel has been described. In this regard, the present disclosure can also be applied to the process of determining whether multiple energy storage modules are connected in parallel within a single energy storage pack. Note that the above-described embodiment assumes an example in which one energy storage module is provided within a single energy storage pack, and therefore the process of determining whether multiple energy storage packs are connected in parallel is synonymous with performing the process of determining whether multiple energy storage modules are connected in parallel.

Mobile bodies powered by interchangeable battery packs 20 are not limited to electric vehicles 1. For example, such mobile bodies also include electric ships. For example, the interchangeable battery pack 20 may be used to power a water bus or water taxi. The battery pack 20 may also supply power to an outboard motor. Such mobile bodies also include trains. For example, a train equipped with an interchangeable battery pack 20 can be used instead of a diesel railcar used on a non-electrified line. Such mobile bodies also include electric flying bodies. Electric flying bodies include multicopters (drones). Such multicopters also include so-called flying cars.

In addition, the embodiment may be specified by the following items.

[Item 1]
A management device (30) that manages a plurality of storage modules (M1) that are connected in parallel to a power source (60, 2) via switches (RY1),
a determination unit (313) that, when at least one of the switches (RY1) in the off state is turned on while the switches (RY1) connected to some of the storage modules (M1) among the plurality of storage modules (M1) are on and the switches (RY1) connected to the remaining storage modules (M1) are off, does not permit turning on of the switch (RY1) if an upper limit value of current or power permitted to be charged to all of the plurality of storage modules (M1) when the switch (RY1) is turned on is lower than a threshold value based on the upper limit value before turning on the switch (RY1);
A management device (30) comprising:
This makes it possible to prevent a decrease in the efficiency of charging the plurality of storage modules (M1) as a whole from the power source (60, 2) due to the new connection of the storage module (M1).
[Item 2]
an acquisition unit (311) that acquires at least an SOC (State Of Charge) for each of the plurality of power storage modules (M1);
a calculation unit (312) that estimates an upper limit value of current or power that is allowed to be charged to all of the plurality of power storage modules (M1) based on an SOC-charge upper limit characteristic that defines the relationship between the SOC of the power storage module (M1) and an upper limit value of current or power that is allowed to be charged to the power storage module (M1),
The SOC-charge upper limit characteristic is a characteristic in which the higher the SOC of the power storage module (M1), the lower the upper limit value of the current or power that is allowed to be charged to the power storage module (M1).
2. The management device (30) according to item 1.
This makes it possible to specify with high accuracy the upper limit of the current or power that is permitted to be charged into the plurality of power storage modules (M1).
[Item 3]
The acquisition unit (311) acquires an OCV (Open Circuit Voltage) of a connection candidate storage module (M1) among the remaining storage modules (M1),
the calculation unit (312) derives an upper limit value of current or power that is permitted to be charged to the power storage module (M1) based on the SOC-charge upper limit characteristic and an SOC (State Of Charge) of the power storage module (M1) connected to the power source (60, 2), and estimates a CCV (Closed Circuit Voltage) of the power storage module (M1) when the power storage module (M1) is charged at the upper limit value;
When the OCV of the connection candidate storage module (M1) is higher than the estimated CCV of the storage module (M1), the determination unit (313) does not permit the switch (RY1) connected to the connection candidate storage module (M1) to be turned on.
3. The management device (30) according to item 2.
This makes it possible to dynamically determine whether or not the charging efficiency from the power source (60, 2) to the plurality of storage modules (M1) as a whole is reduced.
[Item 4]
the calculation unit (312) estimates an upper limit value of current or power that is permitted to be charged to all of the plurality of power storage modules (M1) when the OCV of the power storage module (M1) connected to the power source (60, 2) and the OCV of the power storage module (M1) as a connection candidate correspond to each other after the switch (RY1) connected to the power storage module (M1) as a connection candidate is turned on, based on the SOC-charge upper limit characteristic and the correspondence between the SOC corresponding to the OCV of the power storage module (M1) connected to the power source (60, 2) and the OCV of the power storage module (M1) as a connection candidate;
The determination unit (313) does not permit the switch (RY1) to be turned on when the estimated upper limit value is lower than the upper limit value before turning on the switch (RY1).
4. The management device (30) according to item 2 or 3.
This makes it possible to statically predict whether or not the charging efficiency from the power source (60, 2) to the entire plurality of storage modules (M1) will decrease.
[Item 5]
When the power supply from the power source (60, 2) to the plurality of storage modules (M1) is started, a switch (RY1) connected to a storage module (M1) having the lowest OCV among the plurality of storage modules (M1) is turned on;
Among the storage modules (M1) whose switches (RY1) are in the off state, the storage module (M1) with the lowest OCV is the next candidate for connection whose switch (RY1) should be turned on.
5. The management device (30) according to any one of items 1 to 4.
This makes it possible to connect the plurality of storage modules (M1) in parallel while preventing a decrease in the efficiency of charging the entire plurality of storage modules (M1) from the power source (60, 2).
[Item 6]
a plurality of storage modules (M1) connected in parallel to a power source (60, 2) via switches (RY1);
A management device (30) according to any one of items 1 to 5;
A power supply system (10) comprising:
This makes it possible to realize a power supply system (10) that can prevent a decrease in the charging efficiency from the power source (60, 2) to the entire plurality of storage modules (M1) due to the connection of a new storage module (M1).
[Item 7]
The power source (60, 2) is a motor (60) of the moving object (1) or an external charger (2);
The management device (30) notifies a control unit (40) in the moving body (1) of an upper limit value of current or power that is permitted to be regenerated from the motor (60) to all of the plurality of power storage modules (M1).
7. The power supply system (10) according to item 6,
This makes it possible to prevent the regenerative energy generated by the motor (60) from being wasted.

1 Electric vehicle, 2 Charger, 3 System, 5 Charging cable, 10 Power supply system, 20 Battery pack, 30 Management unit, M1 Battery module, E1-En Cell, 21 Voltage measurement unit, 22 Temperature measurement unit, 23 Current measurement unit, 24 Control unit, 241 SOC-OCV map, 25 Relay drive unit, 31 Processing unit, 311 Acquisition unit, 312 Calculation unit, 313 Determination unit, 314 Notification unit, 32 Memory unit, 322 SOC-charging upper limit current map, 40 Vehicle ECU, 50 Inverter, 60 Motor, 70 AC/DC converter, RYc Main relay, RY1 Pack relay, Rs Shunt resistor, T1, T2 Temperature sensors.

Claims (7)

A management device that manages a plurality of power storage modules that are connected in parallel to a power source via switches,
a determination unit that, when at least one of the switches in the off state is turned on while the switches connected to some of the plurality of power storage modules are on and the switches connected to the remaining power storage modules are off, does not permit the switch to be turned on if an upper limit value of current or power allowed to be charged to all of the plurality of power storage modules when the switch is turned on is lower than a threshold value based on the upper limit value before the switch is turned on;
A management device comprising: an acquisition unit that acquires at least an SOC (State Of Charge) for each of the plurality of power storage modules;
a calculation unit that estimates an upper limit value of current or power that is allowed to be charged to all of the plurality of power storage modules, based on an SOC-charge upper limit characteristic that defines the relationship between the SOC of the power storage module and an upper limit value of current or power that is allowed to be charged to the power storage module,
The SOC-charge upper limit characteristic is a characteristic in which the higher the SOC of the power storage module, the lower the upper limit value of the current or power that is allowed to be charged to the power storage module.
The management device according to claim 1 . the acquisition unit acquires an OCV (Open Circuit Voltage) of a connection candidate power storage module from among the remaining power storage modules;
the calculation unit derives an upper limit value of current or power that is permitted to be charged to the power storage module based on the SOC-charge upper limit characteristic and the SOC of the power storage module connected to the power source, and estimates a CCV (Closed Circuit Voltage) of the power storage module when charging the power storage module at the upper limit value;
the determination unit does not permit turning on of a switch connected to the connection candidate power storage module when the OCV of the connection candidate power storage module is higher than the estimated CCV of the power storage module.
3. The management device according to claim 2. the calculation unit estimates an upper limit value of current or power that is permitted to be charged to all of the plurality of power storage modules when the OCV of the power storage module connected to the power source and the OCV of the power storage module that is a connection candidate correspond to each other after a switch connected to the power storage module that is a connection candidate is turned on, based on the SOC-charge upper limit characteristic, an SOC that corresponds to the OCV of the power storage module connected to the power source, and an SOC that corresponds to the OCV of the power storage module that is a connection candidate;
the determination unit does not permit the switch to be turned on when the estimated upper limit value is lower than the upper limit value before the switch is turned on;
4. The management device according to claim 2 or 3. When starting to supply power from the power source to the plurality of power storage modules, a switch connected to a power storage module having a lowest OCV among the plurality of power storage modules is turned on;
Among the storage modules whose switches are in an off state, the storage module with the lowest OCV is the next candidate for connection whose switch should be turned on.
5. The management device according to claim 1, wherein the management device is a device for managing a plurality of data. a plurality of power storage modules connected in parallel to a power source via switches;
The management device according to any one of claims 1 to 5;
A power supply system comprising: the power source is a motor of a moving object or an external charger;
the management device notifies a control unit in the vehicle of an upper limit value of current or power that is permitted to be regenerated from the motor to all of the plurality of power storage modules;
The power supply system of claim 6.